Introduction to the SFT

[Prajna]

Looking good 👍 maybe some graphite would help against friction on moving parts

Indeed, @Classic. I am looking for some linear slide bearings for the carriages but haven't found something suitable yet. Most linear bearings have a large footprint compared to the bore and are quite weighty. I'm using 5mm rod (probably hardened tool steel if I can find it at a reasonable price), so some linear bearings with a 5mm bore, maybe 10mm outside diameter and as short and light as possible would be suitable but I have not come across such a thing yet.

[Classic]

@Prajna, I don't want to discourage you and I like your easy going approach but as I said from beginning this type of setup require some skillset and pretty good toolset engineering workshop.

Your 5 mm steel rods might not be enough for a rigid build. More likely you'll need some steel pipe/tubes 20-30 mm external diameter with wall thickness 0.5- 1 mm or square steel tubes or similar with a pretty good honed surface for sliding ... following your approach you may want to look up for polished hanger bar for wardrobes but they need at least 3 points fixing at each end and a very good balance of the system not to be wobbly.

Although it may work with 5 mm steel rods as long as you use tension wire from the top to fix it diagonal to the surface where the machine will be placed (like a tent).

Have a look online for a sliding chopsaw and observe the sliding mechanism which suport the whole motor.

Take in consideration vibrations introduced in system and inertia in all moving parts.

Eventually you may think how to adapt some gas shock absorber used in auto industry for easy lift/close of bonnet/boot lid. Maybe a visit to an auto scrap yard may help to find more parts for your build.

I think @Lidmotor on youtube shows how to use some superglue and graphite (pencil) for very low friction ... but you need to find your way for sliding bars. And also, PLA from 3D printing can be hardened with superglue as well.

I like your dedication and conviction and I wish you good luck.

[Prajna]

Thanks @Classic. I'm not sure you have realised the scale I'm working at - the whole device is about a six inch cube. My magnets are tiny, really, 10mm x 5mm disc magnets, so I'm not engineering for big forces and I won't be disappointed if it quickly spins up to a speed that results in its destruction. I want to prove the principle.

I thought superglue and graphite formed a super-strong super-glue, rather like baking soda and super-glue. If it lowers frictional resistance then that might well prove useful. Graphite anyway will help. Polished rods are available for 3D printers etc and tool steel (silver steel) is pretty good stuff because it is rolled to a very close tolerance. Linear bearings would be great, if I can find some that are suitable but graphite and maybe HDPE might work pretty well. Mild steel rod and PLA do not slide very well.

I may have a rather anachronistic approach to development but it seems to work for me, No matter how carefully you think things through there will remain some things that have been overlooked or unknown. A friend pointed out that the unknown is infinite and the known is finite and, no matter how much we learn, that will never change.

At the scale I'm working atm I think 5mm rods will be just fine and if I have to up the size for the next model or mitigate vibration and suchlike, well that is just part of prototyping. Maybe I could be more efficient or do a few engineering calculations before settling on a design but an alternative approach is to cast an engineering eye over the strength of forces you are dealing with and the distances over which they are operating and the materials and tools you have to hand and then you say, "Ok, 5mm rods will do as a first guess."

Thanks for the suggestions.

[Classic]

Also you may consider teflon spray coating for almost no friction ... but I have-no idea how long can last or if it is more efficient or cost wise compared with graphite for a proof of concept prototype.

[Prajna]

I'm still awaiting delivery of a new 3D printer (said to be arriving on Wednesday.) Meanwhile I have been designing the Mk2 version that incorporates a control system.

I've updated the web page for the device detailing the control mechanism that allows the device to be started in forwards or reverse rotation and to be stopped when running. (Just in case anyone is interested.) I'm rather pleased with the way it has turned out and has fitted into the device and I think it is worthy of a patent by itself (if I was into patenting.)

The control system toggles the device off whether it is rotating forwards or backwards, is simple and has few moving parts.

Info at https://tomboy-pink.co.uk/sfmm/